[tex]5\dfrac{42}{170}-3\dfrac{80}{170}=(5-3)+\left(\dfrac{42}{170}-\dfrac{80}{170}\right)\\\\=2+\left(-\dfrac{38}{170}\right)=2-\dfrac{32}{170}=1\dfrac{170}{170}-\dfrac{38}{170}\\\\=1\dfrac{170-38}{170}=1\dfrac{132}{170}=1\dfrac{132:2}{170:2}=1\dfrac{66}{85}[/tex]
[tex]5\dfrac{42}{170}-3\dfrac{80}{170}=4\dfrac{170+42}{170}-3\dfrac{80}{170}\\\\=(4-3)+\left(\dfrac{212}{170}-\dfrac{80}{170}\right)=1+\dfrac{212-80}{170}\\\\=1+\dfrac{132}{170}=1\dfrac{132:2}{170:2}=1\dfrac{66}{85}[/tex]
